Nickel composite hydroxide and method for preparing same

Provided is nickel composite hydroxide containing reduced amounts of sulfate radical and chlorine as impurities. This method comprises a crystallization step for crystallizing in a reaction solution obtained by adding an alkali solution to an aqueous solution including: a mixed aqueous solution including nickel and cobalt; an ammonium ion donor; and an aluminum source, the alkali solution being a mixed aqueous solution of alkali metal hydroxide and carbonate. The ratio of the carbonate to the alkali metal hydroxide in the mixed aqueous solution, i.e. [CO 3 2- ]/[OH - ], is controlled to be 0.002-0.050 inclusive, to thereby obtain nickel composite hydroxide which: is expressed by Ni 1-x-y Co x Al y (OH) 2+α (0.05≤x≤0.35, 0.01≤y≤0.2, x+y<0.4, 0≤α≤0.5); is in the form of spherical secondary particles formed by the aggregation of a plurality of plate-like primary particles, the secondary particles having an average particle diameter of 3-20 µm; and contains 1.0 mass% or less of sulfate radical, 0.5 mass% or less of chlorine, and 1.0-2.5 mass% of carbonate radical.